The present invention relates to a friction joint for connecting mechanical elements, of which at least one has a cylindrical surface.
When connecting together mechanical elements, either in the form of intermediate members arranged, for example, in load carrying or supporting devices, such as frame structures, scaffolding, machines and the like, or forming part of conduit systems for liquid or gaseous media intended to produce sealing, pipe-coupling joints, it has long been the practise to utilize different types of thread joints.
This method, however, renders it necessary to maintain a considerable wall thickness of the tubular elements to be joined, so that the threads do not encroach on the portion of the element material, the dimensions of which must be held continuous so as not to impair the mechanical strength etc. of the elements. With the exception of the relatively short section in which the threads are disposed, this normally implies a waste of relatively expensive material, which has resulted in considerable inventive activity to find ways and means of departing from the principle of thread joints while reducing the wall thickness of the mechanical elements substantially to the dimensions and safety tolerances stipulated with respect to mechanical strength.
In accordance with one proposal, smooth joint surfaces are used, prepared gaps between the surfaces being filled with solder applied in strong, sealing joints with respective surfaces on the joint surfaces.
Although this method has many advantages, the necessity of using additional apparatus such as jointing-metal melting apparatus, and ancillary equipment to enable joints to be made, especially in relatively unaccessible positions, is a disadvantage. Further, this method renders it difficult to make subsequent adjustments to the relative positions of two elements joined together by such a joint, since such adjustments require the joint to be melted down and remade in the adjusted position by re-melting the jointing metal.
In accordance with another, alternative method, a joint is produced between mechanical elements having relatively smooth jointing surfaces with the use of friction creating devices, by means of clamping means. Such devices are often effective for the intended purpose, but in many instances the pressure over the abutting friction surfaces is uneven or is exerted on these surfaces in an unsuitable manner, which may result in a joint of such unreliability as to exclude its use at critical positions. Further, it is often impossible to obtain sufficiently high forces with such joints, whereby normal pressures acting between the friction surfaces is insufficient to maintain the necessary, locking friction forces. Another disadvantage encountered with known clamping devices is that the surfaces of the elements forming part thereof become deformed with repeated use, whereby grooves, scores, burrs etc. are formed on the surfaces and are liable to lock the elements permanently together and prevent convenient subsequent adjustment or dismantling of the elements.
With another alternative, which may be seen as a special embodiment of the aforementioned friction joint, it has been particularly proposed with respect to conduit systems that a strong friction joint is established on one side and on the other side an additional and effective seal is provided against the outflow of media from the conduit system at different conduit coupling joints therein.
In accordance with this alternative, there is used a frustoconical spring ring which is subjected to axial forces while using a cylindrical surface of one element to be joined as an anvil or reaction surface, the axial forces twisting or tilting the spring ring with considerable moments of force. As a result hereof, the relatively, narrow abutment surface of the spring ring will be pressed against the aforementioned cylindrical surface with forces of such magnitude as to cause an extremely strong friction joint between the elements and, at the same time, an extremely effective seal against pressurized media conveyed through the conduit system.
Such a joint presents many advantages, not least because of its simplicity, but, especially with respect to tubular elements, the exceptionally high surface pressure between the normally narrow spring ring abutment surface and the cylindrical surface may cause this latter surface to be deformed in a deleterious manner, e.g. in the case of tubular elements may cause distortion and reforming of the material of said elements, which may be particularly inconvenient or even critical in many instances.